Electron discharge tube and method of manufacture



C. F. MILLER July 22, 1941.

ELECTRON DISCHARGE TUBE'AND METHOD OF MANUFACTURE Filed Nov. 20, 1937INVENTOR 5W? ATTORN Patented July 22, 1941 ELECTRON DISCHARGE TUBE ANDMETHOD OF MANUFACTURE Carl F. Miller, Emporium, Pa., aulgnor to B!-grade Sylvania Corporation, Salem, M, a corporation of MassachusettsApplication November 20, 1937, Serial No. 175,619 8 Claims. (Cl.250-275) tubes and the like and is in the nature of an im- H provementon the tube structures disclosed in U. 8. Patent No. 2,238,025.

A principal object of the invention is to provide an electron dischargedevice of the radio tube typ which is economical to manufacture in largequantities.

Another object is to provide an improved form of stem for a radio tubeand the like, which stem also forms the pronged contact base for thetube.

Another object is to provide an improved method of forming a compositestem-base for a radio tube whereby rigid metal contactprongs can besealed through the stem-base with a minimum of shrinkage."

A further object is to provide an electron discharge tube of the glassbulb type, wherein the electrical elements of the tube areelectrostatically shielded to a maximum extent.

A feature relates to the method of sealing a plurality of rigid metalcontact prongs directly into a composite stem-base, and withoutemploying any special grading glasses or beads between the prongs andthe body of the stem-base.

Another feature relates to an improved method for directly sealinga-plurality of rigid metal contact prongs into a composite stem-base ofa radio tube, whereby low density areas of glass around the prongs areavoided.

Another feature relates to an improved method of forming a compositestem-base for a radio tube with the rigid metal contact prongs sealedtherein in a vacuum-tight manner and disposed around a common center.

A further feature relates to an improved com-- posite stem-base forglass bulb radio tubes wherein the base is formed with a peripheralflange to protect the usual exhaust tubulation.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims.

In the drawing, which represents typical embodiments of the invention,

Fig. 1 is a vertical view, in elevation, of the lower portion of a radiotube embodying features of the invention.

Fig. 2 is a bottom plan view of Fig. 1.

Fig. 3 is a diagrammatic view of apparatus that may be used to form thecomposite stem-base of Fig. 2.

Fig. 4 is a modification of the composite stembase of Figs. 1 and 2.

Fig. 5 is a bottom plan view of Fig. 4.

Fig. 6 shows a modified apparatus for forming the composite stem-bases.

Fig. 'I shows the composite stem-base of Figs. 1 and 2 embodied in atotally shielded radio tube.

Fig. 8 is a modification of the tube of Fig. 7.

Fig. 9 is another modification of Fig. 7.

It has been the usual practice in radio receiving tubes of the glassbulb type, to employ a separate pronged member which is fastened to thebulb, usually by a special basing cement. In other words, the evacuatedor gas-filled glass bulb is usually provided with a reentrant stemterminating in a substantially flat press wherein the relatively thinand soft lead-in wires are sealed. This construction has a number ofdrawbacks which increase very materially the cost of manufacture. One ofthese drawbacks is that because of the flat nature of the press it ispossible to seal the lead-in wires therein in substantially only a.straight line. Consequently in order to make a radio tube of relativelysmall dimensions, it is necessary to have a relatively small press, andtherefore the lead-in wires must be of correspondingly small diameter.Inasmuch as practically all radio receivers are equipped with tubesockets of a standard time. that is with the contacts arranged around acommon center, it becomes necessary to attach to the tube per theseparate pronged base mentioned above. Since the separate base isusually of Bakelite or similar material it is not feasible to exhaustand seal the tube under the ordinary exhaust schedules, with the baseattached thereto, because the temperature of the exhaust schedule wouldruin the material of the base. For these and other reasons, it isnecessary after exhaustion and sealing of the tube, to subject it to anentirely separate basing" operation. Apart from the increased cost ofthe base itself, is the cost of the basing operation which requires thatthe bulb be axially aligned with the base, and then the relatively thinlead-in wires must be threaded into the contact prongs carried by thebase and then soldered thereto.

There is disclosed in my U. S. Patent No. 2,238,025 a tube structurewherein the abovenoted drawbacks are overcome. In general the saidstructure consists 01' a small glass envelope or bulb which has fused orsealed thereto at its lower end, a substantially flat composite stembasethrough which are directly sealed a plurality of rigid rods which extendoutwardly beyondthebasetoservedirectlyascontactprongs, and also extendinwardly of the bulb to serve as support or lead-in connections for thevarious electrodes of the tube mount. This arrangement therefore,completely avoids the usual separate pronged base. However, because ofthe fact that the prongs are sealed directly into the glass base, andsince they are, during the plugging-in of the tube, subjected toconsiderable strains, it becomes important to provide a reliable andeffective vacuum-tight seal between the prongs and the glass bulb base.

I have found that in order to produce the most effective vacuum-tightseal between the contact prongs and the glass base, it is important toavoid any areas of glass of low or non-uniform density in the regionswhere the prongs are sealed. For this purpose there is shown in Fig. 3the preferred manner of effecting the seal-in. A previously preparedglass blank I of the shape shown in Fig. 8 is provided with a centralopening 2 to receive the exhaust tubulation, and a series of smalleropenings 3 to receive the rigid contact prongs l. Preferably the blankis provided with a skirt or rim I. The prongs 4 are placed in thecorresponding openings in the lower chuck member I which may be carriedby a rotatable shaft, and the glass blank i is then assembled over theprongs as shown. The blank is then heated at the regions indicated bythe arrows and during the heating, the chuck i with the blank may berotated. Itwill be understood that any wellknown method of heating theglass to its plastic temperature may be employed, for example heatingtorches may be disposed around the blank or the glass may be heated byelectrical means.

I have found that in order to attain the required uniformity of glassdensity around each prong, it is necessary that the glass be heateduniformly where it is to contact with the prong during the sealingoperation. For this purpose, it is preferable to make the openings 3 inthe glass blank of tapered formation so that the portion of the prongadjacent the chuck I is spaced away from the glass 3 to a greater extentthan is the upper end of the prong. If the openings I were uniform andin substantial contact with the prong throughout their length, when theglass 3 is heated as above described, the lower end of the prong will beat a lower temperature than the upper end because of the heat conductionthrough the chuck 6. By employing slightly tapered openings 3, as theglass 3 is heated, a more uniform temperature gradient is attained inthe area of the glass adjacent each prong.

When the glass becomes plastic, the expansible chuck member 1 and theshaping member I are lowered, whereupon the chuck I is expanded radiallyin any well-known manner thus forcing the molten glass radially outwardand compressing it against the contact prongs which are wetted thereby.If desired, the chuck members 6, I and 8 may be heated to preventstrains being formed in the glass when these parts contact therewith asabove described. The chucks are then separated and upon cooling andannealing in any well-known manner the formed base is removed, with theprongs effectively sealed therein in a vacuum-tight manner. The glassblank is thus provided with an annular shoulder into and through whichthe contact prongs l are directly sealed. Because of the radial pressureexerted on the molten glass by the expansible chuck I, the glass isdistributed around each prong with substantially uniform thickness anduniform density. It will be understood of course that the prongs may beoxidised prior to their insertion into the chuck i, to facilitatesealing as described in detail in U. 8. Patent No. 2.319.- 674.

A short length of exhaust tubing ll '(Fig. l) maythenbesealedto theportion ll of thebase, in alignment with opening I and tipped-of! in anywell-known manner after the bulb has been evacuated. Any well-known typeof radio tube mount or electrode assembly may be connected to the upperends of prongs 4 whereupon the glass bulb or envelope II is assembledover the mount and sealed to the skirt I, as partially shown in Fig. 1.It will be noted that after the exhaust tubulation II is tipped-off, itis protected throughout the greater part of its length by the annularrim 0, and if desired the tubulation may be tipped-o8 so that it doesnot extend downwardly beyond the said rim.

Instead of forming the rim 0 with an annular wall of uniform thickness,as shown in Figs. 4 and 5 this rim may be formed with increasedthickness at the regions where the prongs are sealed therethrough, asindicated by the numeral ll. It will be understood of course that theouter face of the expanding chuck I and the inner face of member I willbe shaped to produce the shape of the rim I as shown in Figs. 4 and 5.

Instead of employing an inner expansible chuck such as chuck 1, and anouter shaping member 8, thus forcing the molten glass radially outward,the glass may be forced radially inward. Such an arrangement ofapparatus is diagrammatically shown in Fig. 8. In this embodiment themember I may be a simple plunger. The outer annular shaped member I! ismade up of a plurality of chuck jaws which are capable of being forcedinwardly in the direction of the arrows to compress the molten glassradially inwards against the contact prongs. In the event that bothinward and outward radial pressures are desired, then both the member Iand the member ll may be expansible, so that as the member I isexpanding radially outward, the member II is being contracted radiallyinward. In either of the embodiments of Figs. 3 or 6 the members I, land the members II, II may be rotated during the expanding operations,if desired.

While the composite stem-base formed as above described, may beincorporated in any well known type of radio tube, certain typicalembodiments are shown in Figs. 7. 8 and 9. Inasmuch as the presentinvention is concerned mainly with the structure of the compositestembase to be incorporated in a glass envelope, it will be obvious thatany well-known form of electrode assembly may be supported on theinwardly projecting ends of the contact prongs. Thus there is shown inFig. 7 an electrode assembly of the triode type comprising theindirectly heated cathode II, a wire-wound control grid I 8 and tubularplate or anode I I. Preferably, although not necessarily, theseelectrodes are assembled as a unitary mount between lower and upper micadisc spacers ll, 20 as described in detail, for example in Patent No.2,084,734. The unitary mount may be supported on the upper ends of theinwardly projecting contact prongs II, 22 as for example by eyeletsfastened into the mica disc II. The electrodes of the mount are thenconnected by short metal wires a,'aso,1sa

to the ends of the respective contact prongs. In

order to shield 'the electrodes electrostatically, after the tube hasbeen subjected to the usual exhaust schedule and the exhaust tubulationIt has been tipped-off. the glass bulb is enclosed in a metal sheathcomprising a metal cup-shaped base member 23 having a series of openingsin its bottom tov allow the contact prongs 2|, 22 etc. to projecttherethrough without being short-circuited. The bottom of member 23 isprovided.

with a circular opening 24 to accommodate the lower end of thetipped-oi! tubulation l0. Preferably there is attached to the bottomo!member 23 a hollow metal boss 2!, having an integral key 23 formed onone side. If desired the member 23, with members 25 and 23 can be formedas one piece from the same metal blank. Welded or otherwise electricallyJoined to the rim of member 23 is an inverted metal cup 21 whichpreferably engages the upper end of the glass bulb [2, thus completingthe electrostatic shielding and preventing rattling of the bulb withinthe sheath. For a detailed description of the member 23, reference maybe had to U. S. Patent No. 2,238,025.

Instead of completing the electrostatic shielding of the glass envelopeby a separate cupshaped member such as member 21, the metal base member23 may be fastened to the glass bulb I2 by a .ring of cement 28, and theglass bulb being provided on its outer surface with a conductive coating29. It will be understood that the coating 23 extends downwardly to oerlap the rim of the base 28 with which it is therefore in electricalconnection, and of course this coating is not applied to the compositestem-base as the rim of member 23 completes the electrostatic shielding.

In certain cases it may be possible to delete the metal base 23entirely. Such an arrangement is shown in Fig. 9 wherein the glass bulbwith the composite stem-base sealed thereto is the same as thecorresponding parts in Fig. 7. In this embodiment, the metal boss 30with its integral key 3| is imbedded in the portion ll of the stem-base,it being understood that the member 30 is imbedded after the exhausttubulation has been tipped-011. The glass bulb is coated on its top andOn its peripheral wall with a conductive material 32 to complete theelectrostatic shielding. Preferably also a conductive connection is madebetween the member 30 and the conductive coating 32, whereby the coatingand member 30 can be grounded or connected to some other suitable basepotential to effect the necessary electrostatic shielding. If desiredthe member 30 may be connected by a metal strap to the particular one o!the contact prongs which is grounded during the normal use of the tube.

While certain specific embodiments of the inventive method and apparatushave been disclosed, it will be understood that various changes andmodifications may be made therein. For example, while the method offorming the composite stem-base has been described as employing apreviously formed glass blank which is heated to render it plastic, atthe sealing-in regions the blank may be formed and the lead wiressimultaneously sealed therein by the process disclosed in U. S. PatentNo. 2,219,574.

What I claim is:

1. A composite unitary stem-base for an electron discharge tubecomprising a glass bottom flattened in a plane substantially transverseto the vertical axis of the tube and having a plurality of rigidconductors directly sealed therethrough in a vacuum-tight manner withthe external ends of said conductors serving directly as rigid contactprongs for the tube. the transverse thiclmess of said bottom beingincreased where the prongs pass and being preformed with transverseperforations toreceive saidprongs so that said glass bottom can bemolded directly around saidtprongs in a vacuum-tight manner, said bottomhaving a substantiallyuniform density of glass in substantially theentire transverse thickness surrounding each prong.

2. A composite stem-base according to claim 1, in which said glassbottom is provided with preformed transverse tapered perforationswhereby said bottom can be molded around said rods to provide seals freefrom glass of nonuniform density.

3. An envelope for an electron-discharge device comprising a thin-walledglass bulb, a preformed composite base and closure for the open end ofsaid bulb comprising a thick glass disc integrally Joined as a unit to athin rim, said rim being sealed directly to the lip of said bulb in avacuum-tight seal, a plurality of rigid metal rods arranged in a circlearound the center of said disc with the material of said disc moldedaround said rods and sealed directly thereto in a vacuum-tight manner,said disc having its transverse thickness materially increased andproportioned where said rods pass therethrough to provide a sufilcientlystrong mechanical support for the externally projecting ends of saidrods, whereby said rods can be used directly as plugin contacts for thetube without danger of weakening said seals and with substantially theentire transverse thickness of the glass surrounding a plurality ofrelatively heavy rigid contact prongs extending through said header withthe material of the header molded around and sealed vacuum-tightdirectly to each conductor the junction between the glass and conductorsbeing extensive to provide a strong mechanical support for the externalends of said prongs with substantially the entire transverse thicknessof the header around each prong being of uniform density.

5. An envelope according to claim 4 in which the central part of saidheader is relatively thin and has sealed thereto a tipped-oil exhausttubulation while the peripheral region of said header has a downwardlyextending thick shoulder to provide a protecting recess for saidtubulation.

6. An electron discharge tube comprising a tubular envelope, arelatively thick glass disclike header sealed vacuum-tight to andclosing one end of said tube, rigid contact pins arranged around thecenter of said header and sealed directly therethrough in a vacuum-tightmanner, the under surface of said header having a shoulder defining acentral recess, and means for shielding said pins comprising a tubularmetal member extending from near the external ends 0! said prongs intosaid recess whereby a substantial part of the length of one of saidprongs in the region passing through said header is electrostaticallyshielded from a substantial part of the length 0! another or said prongsin the region passing through said header.

7. A unitary stem-base tor the bulb of an electron discharge tubecomprising a glass header having a central substantially flatteneddisc-like portion to which an exhaust tubulation is attached, aplurality of rigid conductors sealed directly through said header in acircle around the center thereof, the outer ends of said conductorsserving directly as contact prongs for the tube, said header having onits under face a reentrant

